534 problems solved. Got rejected and hold on 6 months from applying into Amazon. Again very close call, just one dumb interviewer :(

Author: kaidul

Diff for: source-code/Add_Binary.cpp

@@ -0,0 +1,38 @@
+class Solution {
+public:
+    string addBinary(string a, string b) {
+        int n = a.length(), m = b.length();
+        if(n == 0) return b;
+        if(m == 0) return a;
+        string result;
+        int carry = 0, sum;
+        int i = n - 1, j = m - 1;
+        while(i >= 0 and j >= 0) {
+            sum = carry + (int)(a[i--] - '0') + (int)(b[j--] - '0');
+            if(sum == 2) sum = 10;
+            else if(sum == 3) sum = 11;
+            carry = sum / 10;
+            sum %= 10;
+            result += (char)(sum + '0');
+        }
+        while(j >= 0) {
+            sum = (int)(b[j--] - '0') + carry;
+            if(sum == 2) sum = 10;
+            else if(sum == 3) sum = 11;
+            carry = sum / 10;
+            sum %= 10;
+            result += (char)(sum + '0');
+        }
+        while(i >= 0) {
+            sum = (int)(a[i--] - '0') + carry;
+            if(sum == 2) sum = 10;
+            else if(sum == 3) sum = 11;
+            carry = sum / 10;
+            sum %= 10;
+            result += (char)(sum + '0');
+        }
+        if(carry) result += (char)(carry + '0');
+        reverse(result.begin(), result.end());
+        return result;
+    }
+};

Diff for: source-code/Insert_Delete_GetRandom_O(1)-Duplicates_allowed.cpp

@@ -11,10 +11,8 @@ class RandomizedCollection {
 
     /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */
     bool insert(int val) {
-        bool ret = true;
         if(!indices.count(val)) { // indices.find(val) == indices.end() won't work 
             indices[val] = set<int>();
-            ret = false;
         }
         indices[val].insert(values.size());
         values.push_back(val);

Diff for: source-code/Maximum_Average_Subarray_I.cpp

@@ -0,0 +1,18 @@
+class Solution {
+public:
+    double findMaxAverage(vector<int>& nums, int k) {
+        int n = (int)nums.size();
+        if(k > n) return 0;
+        long long sum = 0LL;
+        for(int i = 0; i < k; i++) {
+            sum += nums[i];
+        }
+        double result = (double)sum / k;
+        for(int i = k; i < n; i++) {
+            sum -= nums[i - k];
+            sum += nums[i];
+            result = max(result, (double)sum / k);
+        }
+        return result;
+    }
+};

Diff for: source-code/Remove_Duplicates_from_Sorted_Array_II.cpp

@@ -1,22 +1,11 @@
 class Solution {
 public:
-    int removeDuplicates(int A[], int n) {
-        if(n < 3) return n;
-        int prev = 0, len = n;
-        bool flag = false;
-        for(int i = 1; i < n; ++i) {
-            if(A[prev] == A[i]) {
-                if(!flag) {
-                    ++prev;
-                    A[prev] = A[i];
-                    flag = true;
-                } else {
-                    --len;
-                }
-            } else {
-                A[prev + 1] = A[i];
-                prev++;
-                flag = false;
+    int removeDuplicates(vector<int>& nums) {
+        if(nums.size() <= 2) return nums.size();
+        int len = 2;
+        for(int i = 2; i < nums.size(); i++) {
+            if(nums[len - 2] < nums[i]) {
+                nums[len++] = nums[i];
             }
         }
         return len;

Diff for: source-code/Search_Insert_Position.cpp

@@ -1,18 +1,20 @@
 class Solution {
 public:
-    int searchInsert(int A[], int n, int target) {
+    int searchInsert(vector<int>& A, int target) {
+        int n = (int)A.size();
         if(n == 0) return 0;
-        int start = 0, end = n - 1, mid;
-        while(start < end) {
-            mid = start + (end - start) / 2;
-            if(target < A[mid]) end = mid - 1;
-            else if(target > A[mid]) start = mid + 1;
-            else break;
+        int start = 0, end = n - 1;
+        while(start <= end) {
+            int mid = start + (end - start) / 2;
+            if(target == A[mid]) {
+                return mid;
+            }
+            if(target > A[mid]) {
+                start = mid + 1;
+            } else {
+                end = mid - 1;
+            }
         }
-        if(start >= end) {
-            if(A[start] < target) return start + 1;
-            return start;
-        }
-        return mid;
+        return start;
     }
 };

Diff for: source-code/Search_for_a_Range.cpp

@@ -14,12 +14,11 @@ class Solution {
         int x = -1, y = -1;
         while(start <= end) {
             mid = start + (end - start) / 2;
-            if(A[mid] < target) start = mid + 1;
-            else if(A[mid] > target) end = mid - 1;
-            else { // target == A[mid]
-                if( (mid == 0) or (A[mid - 1] < A[mid]) ) {
-                    x = mid; 
-                    break; 
+            if(A[mid] < target) {
+                start = mid + 1;  
+            } else if(A[mid] >= target) {
+                if(A[mid] == target) {
+                    x = mid;
                 }
                 end = mid - 1;
             }
@@ -31,11 +30,11 @@ class Solution {
         while(start <= end) {
             mid = start + (end - start) / 2;
             if(A[mid] < target) start = mid + 1;
-            else if(A[mid] > target) end = mid - 1;
-            else { // target == A[mid]
-                if( (mid == n - 1) or (A[mid + 1] > A[mid]) ) {
-                    y = mid; 
-                    break; 
+            else if(A[mid] > target) {
+                end = mid - 1;
+            } else if(A[mid] <= target) {
+                if(A[mid] == target) {
+                    y = mid;
                 }
                 start = mid + 1;
             }

Diff for: source-code/Set_Mismatch.cpp

@@ -0,0 +1,47 @@
+// didn't satisfy "firstly find the number occurs twice and then find the number that is missing"
+class Solution {
+public:
+    vector<int> findErrorNums(vector<int>& nums) {
+        int Xor = 0;
+        for(int i = 0, k = 1; i < nums.size(); i++, k++) {
+            Xor ^= nums[i];
+            Xor ^= k;
+        }
+        vector<int> result;
+        for(int i = 0; i < 31; i++) {
+            if(Xor & (1 << i)) {
+                int X = 0;
+                for(int k = 1; k <= nums.size(); k++) {
+                    if(k & (1 << i)) {
+                        X ^= k;
+                    }    
+                }
+                result.push_back(X);
+                int Y = Xor ^ X;
+                result.push_back(Y);
+                break;
+            }
+        }
+        return result;
+    }
+};
+
+class Solution {
+public:
+    vector<int> findErrorNums(vector<int>& nums) {
+        vector<int> result;
+        for(int i = 0; i < nums.size(); i++) {
+            if(nums[abs(nums[i]) - 1] > 0) {
+                nums[abs(nums[i]) - 1] *= -1;
+            } else {
+                result.push_back(abs(nums[i]));
+            }
+        }
+        for(int i = 0; i < nums.size(); i++) {
+            if(nums[i] > 0) {
+                result.push_back(i + 1);
+            }
+        }
+        return result;
+    }
+};